1. Field of the Invention
The present invention relates to an ignition coil supplying a high voltage to a spark plug of an internal combustion engine.
2. Description of the Related Art
An internal combustion engine ignition coil includes a central iron core and a side iron core provided so as to surround the circumference of the central iron core in a coil case. A primary coil connected to a battery is disposed in the outer circumference of the central iron core, and a secondary coil connected to a plug at an interval is disposed in the outer circumference of the primary coil. Aside iron core is disposed at an interval in the outer circumference of the secondary coil. In order to secure insulation properties between the primary coil and the secondary coil and insulation properties between the secondary coil and the side iron core, or the like, the coil case is sealed by an insulating resin.
Miniaturization and a high power are required for an internal combustion engine ignition coil supplying a high voltage for generating spark discharge at a spark plug of an internal combustion engine in an engine for a vehicle or the like in association with fuel consumption regulation enforcement. That is, an ignition coil having high endurance even at a high voltage is required.
Examples of the background art of the present technical field include a technique such as JP-2005-2310-A. JP-2005-2310-A discloses “an ignition coil containing a resin composition containing a thermosetting resin and a filler dispersed in the thermosetting resin, wherein a filler particle size distribution curve represents a small-diameter peak A, a large-diameter peak B having a higher frequency than that of the small-diameter peak A, and a valley C which is positioned between the small-diameter peak A and the large-diameter peak B and has a lower frequency than that of the small-diameter peak A”.
In JP-2005-2310-A, spherical small-diameter particles A are inserted between spherical large-diameter particles B, to improve the flow property of a resin. The improvement in the flow property of the resin provides an improvement in the permeability of the resin between winding wires, which attempts to suppress breakdown in an insulator.